Patent Document 1 discloses a compression self-ignition engine in which a wall surface dividing the combustion chamber is made of a heat-insulating material to reduce cooling loss by the wall surface of the combustion chamber. A reduction in the cooling loss improves thermal efficiency.
Patent Document 2 discloses an outwardly-opening valve injector for injecting the fuel into the combustion chamber of an engine. In the outwardly-opening valve injector, the effective cross-sectional area of a nozzle port, through which the fuel is injected, is changed by changing a lift amount of a valve body. Further, Patent Document 3 discloses a valve covered orifice (VCO) nozzle type injector. The VCO nozzle type injector is configured such that a needle valve is set directly on the seat portion where the nozzle port is open, and that the nozzle port is closed by that needle valve. In the VCO nozzle type injector, the size of a cavitation area, which is generated on the inner periphery of the nozzle port, varies according to the lift amount of the needle valve. Thus, in the VCO nozzle type injector, the effective cross-sectional area of the nozzle port changes according to the lift amount of the needle valve, similarly to the outwardly-opening valve injector.
Patent Document 4 discloses an engine having an outwardly-opening valve injector arranged on the central axis of the cylinder, and injecting the fuel in the form of a cone, wherein the fuel is injected into the cylinder in the second half of a compression stroke, thereby forming, in the combustion chamber, an air-fuel mixture layer and a gas layer (a gas layer containing fresh air) around the air-fuel mixture layer. The engine disclosed in Patent Document 4 reduces the cooling loss by making the gas layer around the air-fuel mixture layer serve as a heat-insulating layer at the combustion of the air-fuel mixture. Patent Document 4 also discloses making the fuel concentration uniform with respect to the fuel injection direction by changing the lift amount of the outwardly-opening valve in the middle of a continuous injection of the fuel.